This invention relates, in general, to heated fusing roller apparatus for affixing toner material to a substrate to form permanent images thereon and, more particularly, to means for controlling the power input to the heated roller for maintaining substantially constant the surface temperature of the heated roller at an area where it contacts the toner material.
In the process of electrostatic or magnetic printing, information is typically recorded in the form of a latent electrostatic or magnetic image on a recording member with subsequent rendering of the latent image visible by the application of electrostatic and/or magnetic marking particles, commonly referred to as toner. The visual image can be either fixed directly upon the recording member or transferred from the member to a sheet of plain paper with subsequent affixing of the image thereto.
In order to permanently affix or fuse a toner material onto a record medium, such as paper, it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become adhesive. This action causes the toner to be absorbed to some extent into the fibers of the record medium. Pressure is sometimes used to increase the adhesive. Thereafter, as the toner material is cooled, solidification of the toner material occurs causing the toner material to be firmly bonded to the record medium.
In both the electrostatic and magnetic printing arts, the use of thermal energy for fixing toner images onto a support member is old and well-known.
One approach to thermal fusing of toner images onto a record medium has been to pass the record medium with the toner images thereon between a pair of opposed rollers, at least one of which is either externally or internally heated. In this type of arrangement, the toner image contacts the surface of the heated roller member in the nip between rollers to thereby produce heating of the toner image within the nip.
In apparatus utilizing a fuser roller pair as described above, it is important that the heated roller surface be maintained within a suitable range to properly fuse the toner image to its record medium. A conventional manner for accomplishing the foregoing is by the employment of a temperature sensitive device which is coupled to the heated roller and whose output controls the heat source. A suitable arrangement is described in my copending application entitled "Non-Contact Temperature Sensor For a Fusing Roller" filed concurrently with this application and assigned to a common assignee. Where AC power is involved the output either switches power on or off completely until the roller temperature reaches a desired level or switches different partial cycles of power as by an SCR until the desired temperature level is reached.
These prior art arrangements have exhibited shortcomings. Some of these have produced overshoots and undershoots of temperature beyond the desired narrow range of desirable temperatures. Others have generated objectionable high frequency noise or DC components in the power line, peak power requirements, transients, etc.
Accordingly, it is a primary object of this invention to provide a new and improved method and apparatus for controlling the heat used to fuse toner images to the record medium.
Another object of this invention is to provide an improved arrangement for controlling the temperature of rotating rollers or other machinery.
Still another object of the present invention is to provide a new and improved arrangement for controlling the temperature of the heated fuser roller in a toner imaging system.
Yet another object of this invention is to provide a new and improved control circuit for controlling electrical energy supplied to a thermal servo system load.